Booster for relatively insensitive explosives



June 5, 1962 M. A. COOK ETAL 3,037,452

BOOSTER FOR RELATIVELY INSENSITIVE EXPLOSIVES Filed Oct. 17, 1958 INVENTORS MELVIN A. COOK HE NR) E FARNAM. JR. STANLEY W/NF/ELD BY ATTORNEYS D. MALSTROM l'l. PETERSON United States Patent 3,037,452 BOOSTER FOR RELATIVELY INSENSITIVE EXPLOSIVES Melvin A. Cook, Salt Lake City, Utah, Henry E. Farnam, Jr., Seven Islands, Quebec, Canada, and Stanley D. Malstrom, Salt Lake City, and Winfield H. Peterson, Provo, Utah, assignors, by mesne assignments, to Intermountain Research and Engineering Company, Inc,

Salt Lake City, Utah, a corporation of Utah Filed Oct. 17, 1958, Ser. No. 767,835

4 Claims. (Cl. 10224) This invention relates to detonating means for explosives and more particularly to boosters for relatively insensitive explosive compositions.

Insensitive explosives, containing a high percentage of ammonium nitrate and containing nonexplosive organic sensitizers, have found wide application as blasting explosives. Prilled ammonium nitrate containing 94 percent ammonium nitrate and 6 percent fuel oil and aqueous slurries of coarse TNT-ammonium nitrate are examples of such insensitive explosives. Such compositions are not detonatable by blasting caps and prior art methods for detonating them include the use of dynamite or relatively large quantities of fine-grained TNT primers, for example, which are detonated by blasting caps or Primacord. These methods suffer from the disadvantage of being expensive and further, dynamites, fine TNT and blasting caps are very sensitive to heat and shock.

In modern large diameter blasting operations using high ammonium nitrate explosives, Primacord fuse is the most desirable detonator. The high ammonium nitrate explosives are not dependably detonatable by Primacord, however, and require a booster. Unfortunately, only a few of the most sensitive explosives are consistently capable of detonation by Primacord containing the minimum content of PETN, e.g., about 50 grains of PETN per foot of Primacord. Of those boosters that are operable, relatively large quantities of expensive boostering compositions are required consistently to booster the ammonium nitrate explosive.

Accordingly, it is an object of the present invention to provide a booster for insensitive explosives which is consistently detonatable by minimum PETN content Primacord.

It is another object of the invention to provide such a booster which consistently detonates high ammonium nitrate explosives in either the wet or dry state.

A further object of the invention is to provide such a booster which is inexpensive and utilizes a minimum of the expensive Primacord-sensitive materials.

Among the other objects of the invention, one is to provide a protected core booster in which Primacord is readily and simply threaded for use in blasting operations.

Another object of the invention is to provide a booster which is much less sensitive to heat, shock, impact, friction and other influences causing accidental initiation than prior art boosters.

We have now found that the most important factor in a booster with respect to its boostering activity on insensitive explosives is its detonation pressure or brisance. The term brisance connotes shattering action which is dependent on the detonation pressure. In the hydrodynamic theory of detonation, the detonation pressure is proportional to the density of the explosive and the square of the detonation velocity.

Examples of explosives of high brisance are cast or pressed pentolite (PETN-TNT), TNT, tetryl, tetrytol (tetryl-TNT) cyclotol (RDX-TNT), composition B (RDX-TNT-wax) and Ednatol (EDNA-TNT). The more inexpensive of these explosives are not detonatable by Primacord, however.

It has been found that PETN, PETN-TNT mixtures,

"ice

RDX and cyclotol are detonated by Primacord, but their high cost and the relatively large quantities required make it uneconomical to use them as boosters.

In accordance with the invention, we provide a booster for detonating insensitive blasting charges comprising a compacted core of Primacord-sensitive explosive material surrounded by a compacted sheath of Primacord-insensitive explosive material of high brisance, said booster having at least one perforation extending through said sheath and said core adapted to receive a detonating fuse. A preferred embodiment is one in which the core is cylindrical and an annular sheath of Primacord-insensitive material surrounds the core. One of the preferred embodiments comprises a cast 50/50 pentolite core and a cast TNT sheath.

FIGURE 1 illustrates a booster made in accordance with the invention.

FIGURE 2 is a cross-section taken on lines 22 of FIGURE 1.

FIGURE 3 is a cross-section taken on lines 3-3 of FIGURE 1.

The booster is indicated at 10 and comprises a compact core 12 of Primacord-sensitive material surrounded by a sheath 11 of Primacord-insensitive material of high brisance. In the embodiment shown, two holes 13 extend through the sheath and the core for receiving Primacord detonating fuse.

While the assembly may assume any desired shape, it is preferred to use the cylindrical form shown for economy of material and ease of manufacture. The core and sheath may be either cast or pressed and may be manufactured by positioning the core 12 in a mold and casting or pressing the sheath 11 around it. The holes 13 may be drilled through the assembly or the assembly formed by forming the core 12. around pins corresponding to the holes, utilizing the pins to position the core symmetrically in a mold, forming the sheath around the core, and then removing the pins to form the holes.

In use, a Primacord fuse, such as 50 grain PETN/ft., is threaded through one or more of the holes 13 and knotted to prevent the removal of the booster from the fuse. The booster may be inserted in a priming cartridge of ammonium nitrate explosive, or preferably lowered by itself into the bore hole by suspending it on the Primacord line at the appropriate position in the hole. Then the main charge is introduced simply by pouring the loose or slurry explosive into the hole. The Primacord fuse is initiated electrically as is well known in the art.

As examples of the superior boostering action of the booster of the invention, boosters illustrated in FIG- URES 13 were prepared, utilizing a core cast of 30 grams of 50/50 pentolite and a sheath cast of 220 grams TNT. The core size was about 1.25 inches in diameter and 1.25 inches long. The overall size of the sheath was 2.25 inches and 2.25 inches long. One hole was A inch in diameter for receiving Primacord and the other 7 inch in diameter for alternatively receiving an electric blasting cap or Primacord of a larger size as desired. Such boosters have been found consistently to booster 94/ 6 ammonium nitrate-fuel oil and 64/21/15 ammonium nitratecoarse TNT-water mixtures when initiated by 50 grain Primacord. The equivalent booster consisting wholly of 50/50 pentolite also applicable for consistent detonation of these explosives was found to be grams, containing 87.5 grams of PETN. In contrast to this, the above boosters of the invention contain only 15 grams of the expensive PETN.

The above dimensions for a cylindrical booster of the invention have been found to 'be optimum when using a cast 50/50 pentolite core and a cast TNT sheath. The core should contain about 2530 grams of pentolite. The core size may be in the range of 0.75 to 1.5 inches in diameter (but not exceeding about 0.6 times the sheath diameter) and 1.0 to 1.5 inches long (but not exceeding about 1 inch less than the sheath length). The sheath size may range from 2 4 inches in diameter and 2-4 inches in length, with regard for the above core size qualifications. In other words, the core size is substantially fixed at a minimum and the sheath volume must be at least about 4 to 5 times the core volume but may be larger, although for economic reasons, it is preferred to utilize as little TNT as will provide consistently operative boosters.

' Other Primacord-sensitive materials may be used for the core, such as pentolites containing less than 50 percent PE'IN; with /90 pentolite, we have found that about 50-60 grams are necessary to provide consistent boostering. Likewise, other Primacord-insensitive materials may be utilized for the sheath.

As pointed out, either cast or pressed boosters may be prepared in accordance with the invention. However, cast boosters are preferred as they do not crumble when they become wet or subject to rough handling. Cast boosters are also less water-sensitive when used under water.

We have thus described novel boosters which are consistently operative for boostering ammonium nitrate ex plosives, which employ a minimumof expensive mate- A rials and which are consistently detonatable by 50 grain Primacord. While the invention has been described in terms of certain embodiments, these are to be considered illustrative rather than limiting and it is intended to cover all further embodiments that fall within the spirit and scope of the appended claims.

What is claimed is:

1. A booster for detonating a mass of blasting explosive insensitive to blasting caps comprising a compacted core of Primacord-sensitive explosive surrounded by a compacted sheath of highly brisant Primacord-insensitive explosive, said booster having at least one perf0ra tion extending through said sheath and said core adapted to receive a detonating fuse, themass of said core being equivalent to a cylindrical block of 50/50 pentolite 0.75 to 1.5 inches in diameter and 1.0 to 1.5 inches long, and the mass of said sheath and core being equivalent to a cylindrical block of trinitrotoluene 2 to 4 inches in diameter and 2 to 4 inches long.

2. The booster set forth in claim 1 wherein said core comprises cast 50/50 pentolite and said sheath comprises cast trinitrotoluene.

3. The booster set forth in claim 1 wherein said core comprises to grams of /50 pentolite, said sheath com-prises cast trinitrotoluene, and wherein the volume of trinitrotoluene is at least four times the volume of the core.

4. The booster set forth in claim 1 wherein said core is a cylinder of cast 50/50 pentolite, about 1.25 inches in diameter and about 1.25 inches long, and wherein said sheathis a cast cylinder of trinitrotoluene, about 2.25 inches in diameter and about 2.25 inches long.

References Cited in the file of this patent UNITED STATES PATENTS 231,348 Nobel Aug. 17, 1880 1,652,961 Smelling Dec. 13, 1927 2,733,658 Moat Feb. 17, 1956 2,775,200 Guenter Dec. 25, 1956 2,777,389 Lawrence Jan. 15, 1957 2,785,633 Ewing et a1 Mar.19, 1957 

1. A BOOSTER FOR DETONATING A MASS OF BLASTING EXPLOSIVE INSENSITIVE TO BLASTING CAPS COMPRISING A COMPACTED CORE OF PRIMACORD-SENSITIVE SURROUNDED BY A COMPACTED SHEATH OF HIGHLY BRISANT PRIMACORD-INSENSITIVE EXPLOSIVE, SAID BOOSTER HAVING AT LEAST ONE PERFORTION EXTENDING THROUGH SAID SHEATH AND SAID CORE ADAPTED 